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To what extent is it viable to launch manned gliders vertically using unmanned drones rather than tow planes?
An electric, vertical takeoff drone lifts a manned glider 5 km in the air. The glider is then released from the drone, and glides 50 km to carry its passengers across a lake. The drone meanwhile simply descends vertically back to the ground to where it took off from, without passengers or a pilot on board.
Would this sort of “glide slide” be viable? Is it a way of realizing the advantages of electric flight (in niche situations, for very short flights across physical barriers like Great Lakes) while minimizing the problem of battery weight? And of realizing the benefits of gliding without needing a towplane (which in turn requires a second pilot, a runaway, etc.)?
[Or perhaps, alternatively, instead of having a vertical takeoff drone lift a glider, you could have an electric plane which takes off on a runway but then drops its batteries by parachute back down to earth once the plane reaches altitude, and then the plane glides the rest of the way...]
And what about pushing the concept to far more extreme lengths even? Instead of rising vertically 5 km and then gliding 50 km diagonally back down to earth, what about a (much smaller) glider being lifted 20 km vertically and then gliding 1000 km across?
I know nothing, so would love some feedback here.

All you suggest is feasible, getting certified for commercial carriage of passengers is another thing entirely.  I'm pretty sure the FAA would frown on the lack of missed approach capability.

Boeing experimented with a strategy to launch a parachute via rocket, and then use that as a winch point in the sky. A rope would connect the falling parachute to a glider on the ground on one end, and a winch on the other. (To others at SE.Aviation: I forget the name of this program, so sadly cannot find references for it. Please drop it in a comment if you know it.)
Possibly a more viable strategy would be to have a parachute which is held aloft by a balloon. The same principle applies, which is that the winch point is in the sky and so launches wind up much, much higher. However, in this scenario after every launch the balloon returns the parachute to its maximum height, thus allowing repeated launches for (almost) no more energy than is required to satisfy the glider's potential and kinetic energy gains.
Modern gliders reach 60:1 glide ratios or better. Even a 787 has a 20:1 glide ratio. So 5km height would be amply sufficient to go 50km, with all but the strongest headwinds.
Michael Hall's excellent point that the FAA wouldn't appreciate the lack of go-rounds is arguably met by having a system which has just enough battery power to execute a go-round. There are plenty of motorgliders which can validate the concept.

You need to subtract the kinetic energy to get the glider to best glide speed from the potential energy added by lifting the glider up. Say the best glide speed is 50m/s then this altitude is 130 m without conversion losses. I would at least double this for realistic figures.

@PeterKämpf I think this is what I was saying, but I added the word "glider's" to clarify that section. Let me know if this is different from what you meant.

With a cheap source of electricity the concept might be viable, if only for tourist flights.
Another approach might be with a balloon.  Here the lift is free and great heights are possible.
Or, perhaps, a combination of the 2 using electric props, an aerodynamicly shaped dirigible, and solar cells as sustainers.
A realistic glide ratio for starters may be 1:15 to 1:20, so 20 km lift could be around 300 km glide, not 1000.
Using a battery pack to climb, and then dropping it?
Surprisingly, this will not affect the glide range.  Reducing weight once you're up there only throws away potential energy that can be used for a faster glide.  And, if you keep your batteries, the glide could be "stretched" quite a bit with some propulsion.
If the plane can lift all the weight to extreme altitude, with batteries, it may be better just to have a charger at the destination.
However, climbing to higher altitudes does have advantages on longer trips.  Extra energy climbing to altitude must be weighed against energy savings at that altitude$^1$.  Airliners these days take this approach all the time, with the added bonus of being able to fly over bad weather most of the time.
$^1$ true air speed is greater than indicated airspeed in thinner air

That's great, thanks very much for the answer. I had considered the balloon idea, but wasn't sure it could be done safely or comfortably for passengers... what do you think?
And I guess more importantly, how big might the aircraft be? If you were okay with a very low glide ratio, could you have a high passenger capacity? Hypothetically,
could a high-passenger-capacity plane cross a Great Lake (40 km, say)  from a 20 km-altitude balloon?

Look into the lifting capacities of the airships from the 1920s to 1930s.  The $Hindenburg$ could lift over 200 tons, and modern swiveling electric motors with aerodynamic shaping would only add more, especially with a runway.

One might start at 12 km, with a very modest 10 to 1 glide ratio.  Remember, from a balloon drop, an initial dive is needed to gain best gliding speed.  From the altitude where this speed is attained with the plane stabilized on its glide path, apply the glide ratio to get your distance.

Would it be possible for the glider to take off vertically from the balloon, so as to give the passengers a more comfortable ride - in other words, to avoid the dive? And could a balloon that is only intended to move vertically for the most part (unlike the Hindenburg) be built in such a way as to have a much larger lift capacity?

A very large carrier could support a launch system, almost like an airborne "flat top".  Bouyant lift could support the carrier, but the issue would be how to land it after dropping the glider.  The combination of aerodynamic lift for the glider and bouyant lift for the carrier (hybrid airship) seems the most feasible approach for now.

Interesting, thanks. An alternative, scaled down version idea: what if you had a glider lifted vertically by a crane (or tethered balloon, etc.), say 500 metres in the air. Could there be a way for the glider to take off from the crane without needing to go into a dive? Could it take off vertically from the crane in a way comfortable for the passengers? This could be for a 5-10 km crossing maybe, for locations where bridge or ferry or tunnel transport alternatives aren't viable for one reason or another...

@JshupacFuture-Economics. Aircraft need forward velocity to fly.  The advantages of flying high can also be scaled up to sub-orbital applications as well.  Other ideas could include a ground based tow-release system.  But, it is best to fully understand the current system.  Airliners lug their fuel and engines to higher altitude by themselves, with the descent essentially a glide.  For trips less than 300 km, they simply take less fuel, leaving more room for cargo and passengers.  Airliners are essentially giant gliders (ratio > 15:1).

But, for an eVTOL aircraft, for extremely short flights, would it be possible to maximize passenger capacity and passenger comfort by taking off vertically from a crane, so as to avoid lugging fuel or lugging big batteries, and to avoid the aircraft having to go into a dive at the start of the flight?

@JshupacFuture-Economics you are essentially talking about a 2 stage flight system.  Costs building and maintaining must be evaluated against current systems.  Sure, with enough $$$,  but it must clear hurdles 2 and 3, is there a demand, and is the approach more cost effective.  Scale models may help move your concept forward.  Good luck!

Here's a video of a glider being released from a hot air balloon. https://youtube.com/shorts/vU_2yjQpSWo?feature=share


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How can I calculate torsional stiffness of a wing when the dimensions of the cross section vary?
I am working on a project and we need to calculate the torsional stiffness of a wing in order to analyze flutter and divergence. However, the dimensions of the cross section vary along the semi-span, so the torsional stiffness changes. How can I calculate this in this situation?

Basically, you can take two different paths as a starting point.

From the FEM model of the wing, from the axis (I assume it is the y-axis), where the torsion movement occurs, you can find the value of Iyy. Then, by looking at the mode shapes and finding first torsional mode shape frequency, you can calculate kt from the formula wn=sqrt(kt/Iyy) from the frequency you see for the 1.torsion mode. Of course, since other modes also have a contribution, even if it is not a completely correct answer, it may work at the beginning.

Twist can be read by applying unit moment from tip of the wing. Then kt can be calculated from the formula: unit moment=kt * theta. It's not the exact equivalent stiffness of course, but it's a simple starting point.

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Where is it documented an airport is military?
On sectional charts (at least in the US) military airports appear with the same symbols as public airports, eg. KBKF.  Some military bases are within restricted airspace.  I would assume all military airports are restricted to public use.
Is there a way to see this on the sectional chart?  Would this information be found in the A/FD?  Is it just assumed that AFB, NAS, etc. indicates military?

Generally information on restrictions for any charted airport can be found in the A/FD (look for RSTD or the magic word PPR - Prior Permission Required - in the remarks). For example, KBKF is restricted, prior permission is required if you're not based there, and you need to let them know at least 24 hours in advance that you would like to land there: https://i.sstatic.net/fMU08.png

@voretaq7 Thanks for your comment. This seems like an answer.  Why not change your comment into an answer?  ;)

After reading the answers here, the question should be "why aren't military airfields designated in a more prominent way?"

All navy airfields are designated KN(XX).  In fact, only navy airfields, under the ICAO system, start with KN.  Also, there are many joint use airfields that are both civilian and military, such as KNYL (MCAS Yuma/ Yuma Intl), and you can land there until you're blue in the face.  However, generally speaking, its best to leave military bases alone.  We operate under very rigid and expected procedures, and random traffic in the area quickly becomes dangerous and unpredictable.  Imagine your surprise when I enter the pattern at 350+kts...

Agreed regarding many joint fields. For example, both Knoxville McGee-Tyson (KTYS) and Nashville International Airport (KBNA) have military aircraft based at the field. KTYS used to have a bunch of fighters based on site back during the Cold War to protect the nearby nuclear research and production facilities at Oak Ridge.

AFB, MCAS, NAS, CGAS/CGS, and AAF would always be military, yes. BUT the lack of that in the name doesn't mean it's not military... Outside the US especially there's often no such thing to indicate a military base from a civilian field (though AB (for AirBase) is at times used).
How do you know? You're supposed to know where you're going when you're flying, and that includes what's off limits to you.
http://www.post8.org/images/secchart.jpg shows the legend of a sectional (can't inline the image, SO refuses to), which says clearly "All military airports are indicated by abbreviations AFB, NAS, AAF, etc. For complete airport information consult DOD FLIP". So how do you know? The chart tells you by the name of the facility. It also shows a double ring instead of runway icons as indicating military, but on some charts I looked at that appears to not be consistently applied.

Looking at SkyVector the military bases in Europe have [Mil] suffix on the VFR chart. The ones in USA can only be recognized by the bajillion abbreviations like AFB, NAS, AAF (MCAS…)….

From other places I knew where to look for some military airport in Japan there is also the [Mil] suffix and in India the military airports seem to be omitted from the sectional chart altogether (on SkyVector; other sectional chart makers may differ, of course).

Maybe I'm interpreting the legend wrong, but I think that the double ring symbol only indicates military airports with "other than hard surface" runways.  Military airports with hard-surface runways would use the standard symbols.  For example, Bicycle Lake AAF (BYS) has the double ring and is listed as having a gravel runway.  USMC Sweetwater (NV72) is another example, just a 3700' dirt strip in the middle of nowhere.

@Brian possibly, would make sense.

The definitive reference in the US is the A/FD. The A/FD shows the "operating agency" of each airport if it isn't a civil, public airport:

Airports within this directory are classified into two categories,
  Military/Federal Government and Civil airports open to the general
  public, plus selected private use airports. The operating agency is
  shown for military, private use and joint civil/military airports.

So if you don't see an operating agency, it's civil. If you do, then you need to consult the list of possible agencies. For example, KATL has no operating agency so it's civil and public; KMGE (Dobbins ARB) has the operating agency "AFRC (AR ARNG)" listed in the A/FD which according to the legend means "Air Force Reserve Command (US Army Reserve US Army National Guard)".

If it's a dedicated military airfield, then they do limit what you can do there. If their not busy(basically, nothing based there's flying much), you can often times coordinate to do approaches there, as long as you don't land. If something comes up and you declare an emergency and land, expect to be met by lots of people pointing guns at you, and to be detained for awhile. Transitions are usually easy, to coordinate through talking on the Tower frequency, or talking with the area's approach to go through any airbase delta... usually.
REF: BKF, don't bother with asking for approaches there, due to the tight confines of airspace with DEN, FTG, and APA.

This doesn't answer the question, which is essentially "I see an airport on the map -- how can I tell if it's a military base or a public airport?" not "What can a member of the public do at a military airfield?"

@DavidRicherby look at the edit on the OP this answer was posted before that change happened.

Ah. It's unfortunate when questions change in a way that invalidates answers. But, still, this isn't an answer to the question that's been asked; it could, perhaps, be reposted as an answer here (the version of this question that slookabill was answering was closed as a duplicate of that question).

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Why were the toggle switch guards in the Space Shuttle titanium?
I recently found out that the little protective rails over the toggle switches in the space shuttle were made out of titanium.  I'm not sure of which alloy specifically, but probably 6AL4V (or "Grade 5").  I heard rumors that the covers for each switch cost near $800 (USD).  Titanium is heavier than aluminum, so what was the reasoning for using it to make the switch covers?
All I can think of, is in the event of a crash the titanium would better protect the switches than aluminum...  But I'm not sure how high that is on their list of concerns in the event of a crash, or similar event.

uhm, maybe this should go to space.se?

Just a guess but it could be related to aluminium alloys being more vulnerable to fatigue and deformation. I think modern alloys are good enough, but at the time the space shuttle was designed, I think there was a real concern for the guards starting to bend after some use. And once you have bought the necessary number of 800 dollar titanium switch guards, you'll never need to buy any 20 dollar anodized aluminium replacements.

aluminium is a very soft metal, I guess. you can smash it with a punch

Why do you say titanium is heavier? Titanium has bigger density than aluminium, but has twice its strength... so pieces of titanium will be lighter for the same resistance needed. Also titanium has higer fusion temperature, so higher temperature resistance, but also vulnerable to fire.

@Ville Niemi, I bet you're right.  I didn't think about the difference in time since it was built to modern day.

Honestly, I don't see a problem with this question here.  I think that it is more on topic here than on space.se.  I am asking about the actual craft (albeit, spacecraft), not about space "exploration."

I agree with Sponge Bob and feel that the space shuttle is part of "aviation" as well as "space exploration", and the question would be suitable on either site.

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Do runways need to be repaired after gear up landings?
There have been may cases of civilian, commercial, and military flights that have either been forced to or accidentally landed gear up.
When this happens I imagine that it can do serious damage to the runway it's landing on (assuming it's landing on a paved runway).
Does the runway need to be repaired after such a landing, if so, how long does it take, and how extensive are the repairs?
These are some of the different scenarios that come to mind:

Civilian aircraft doing a gear up landing, maybe about 1500-5000lb or so.
Commercial airliner doing a full gear up landing.
Commercial airliner with a single broken wheel.

How would runway repair be conduced in these scenarios?

Your new photo is Engineered materials arrestor system i.e. not normal runway construction.

… and the landing on the photo was a gear down landing. The three dug trails are behind the gears.

Runways are usually made of several feet of reinforced concrete. Any damage to them after a wheels-up landing is superficial at best. Details depend on circumstances, but in general light aircraft will cause less damage. A full wheels-up landing is rather easy on the runway: The aircraft's fuselage and wing fairing structure are flexible and malleable, so it will buckle and bend until the local surface pressure is too low to cause more bending. To really damage a concrete surface you would need carbide tools, not sheet aluminum.
An unwheeled landing gear strut of an airliner is probably the worst scenario. The Airbus in the linked video had only a damaged nose gear, which carries a small fraction of the total load, and you will see in the close-up at the end of the video that the runway did not suffer. A similarly damaged main gear, however, will cut a groove.
All what is needed for repair is some fast-curing liquid for filling the nicks and scratches and some paint to repair the runway markings.
If you land a composite aircraft wheels-up, the concrete will act like sandpaper on the structure. The landing zone will be marked by white epoxy dust. A broom is all what is needed to put the strip back to its initial condition.

Some runways are 4 feet thick, depending on the traffic, and even thicker, I think, at the ends.

I changed the photo in the original question.  In your answer, you make it seem like gear up landings don't really damage runways very much.  What about in the photo?  And I've heard of special runways that actually are made of soft cement to help arrest a "runaway" airplane.

What about asphalt runways, which are very common.  (For example, Europe's busiest airports -- Heathrow, Frankfurt, Charles de Gaulle and Amsterdam Schiphol -- all have asphalt runways.)

@DavidRicherby: What is below the asphalt? I always thought that the asphalt is only the top coat, and below is reinforced concrete.

@PeterKämpf I don't know. To add to the conclusion, Wikipedia describes some of Chicago O'Hare's runways as "asphalt", some as "concrete" and some "asphalt/concrete".

@Keegan: That's an EMAS, which is designed to be damaged (to help stop the aircraft).  The actual runway generally isn't damaged all that much.

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During night flying, which color lens for a flashlight is most beneficial?
I went on a night flight tonight after not flying for a few months.  I didn't have any monochrome lights, so I actually just covered a flashlight of mine with red athletic tape (which acted as a filter really well).
I know that using monochrome is the most important thing about preserving night vision - but does it particularly matter, while flying, which color I use?

astronomers and astrophiles use red light as it will disturb the retina as little as possible.
http://www.atmob.org/about/clubhouse/red-light-etiquette.pdf

You will want to use red light.
Why?
See Does red light preserve your night vision? on the Biology StackExchange for a good explanation of the biology and physiology involved, and how it relates to perceptual ability.
As stated in this answer (by leonardo) to that question:

If one is exposed to red light (above ~650 nm), it would activate the L-type cones mainly (possibly some M-type activation), but no rod activation. Rods are the low light receptor cells in our eyes, and as such, are very sensitive to the photon density, or brightness, entering the eye.
This is just my speculation, but I think it's plausible that if you were in a completely dark environment with just a red light, filtering out the higher frequencies, night vision could be spared in the sense that we don't activate the rod cells.

Thanks!  I guess I'll keep it below 650.  Cree has a few colored LED options - their Amber-595nm, Red/Orange-620nm and the Red-630.  Does this mean using the Amber will preserve night vision better than the others?

Note that you'll probably need a plain white flashlight anyway -- as abelenky points out red is a lousy light for color discrimination (charts and gauges should be illuminated with a light that lets you see colors). Red/White LED flashlights are easy to find (I personally like bicycle headlamps for this purpose since you can usually dim the white light).

@SpongeBob: Higher frequencies are shorter wavelengths, so 595nm is a higher frequency than 630nm. The important thing to note is that activating rods (about 600nm and shorter) causes the rhodopsin in your eyes to bleach (which means you lose your night vision). Since the cones do not help you see detail, they are not useful for things like reading instruments or maps. So you want to minimize your rod exposure while maximizing your cone exposure. Your eye has more red cones than any other color, so using red light makes the most sense.

Oh.  My bad.  I just assumed you meant above 650nm wavelength... since that's what the answer says.  But you really meant above the frequency of light with a wavelength of 650nm.  Basically visible light between IR and 650nm is best for preserving night vision.  I edited the answer to show frequency instead of wavelength so it's not as confusing.

@SpongeBob If you believe that your edit is accurate, you really should make it on the original answer as well. Right now the quote disagrees with the original. Personally I find your edit confusing; "above X frequency" is equal to "shorter than Y wavelength" where for appropriate units Y=c/X, and as you reduce the wavelength of visible light, you go from red (at the long wavelength end of the spectrum) to blue and ultimately violet (at the short wavelength end). So saying "above 461 THz" is very different from saying "above 650 nm". Light is also commonly discussed in terms of wavelength.

@SpongeBob Your edit is wrong. "Above 650nm" is both the correct phrasing and the logical unit (nm) to use.  "Above" means higher, longer, or greater -> in the direction of infrared if we are talking about wavelength.  By changing the unit to frequency, "above" now still means higher, but this instead means faster -> in the direction of shorter wavelength or towards blue and UV.  Also, as a scientist and engineer who has worked with optics and visible light for many years, never have I seen anyone use THz as a working unit. Frequency is popular in some EM ranges, but not this one.

Sorry.  My bad.  I don't know why I was so confused.  You are all right.

I know everyone is going to say you need a red light, and that should be your primary light.   But I think its important to also have a white light and one other color (typically green).
The reason is simply that red light makes everything look red, and makes it hard to distinguish colors!  Can you actually verify that the AVgas is light blue when you look at it under a red light?  Can you see bright red, important items on a checklist?  Reading red-text against a white background can be very difficult with a red light.  On a VFR map, airport symbols are blue or magenta to indicate towered/untowered airports, but they both look the same under a red light.
So while your primary light should probably be red, you'll need alternate colors and plain-old white for many things.

There are some headlamps available on the cheap that allow you to switch between red and white light as needed. And they're hands-free too.


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What are the component terms that make up this pressure altitude calculation?
I am a bit confused by pressure altitude, in my ground school we were taught and equation ((29.92 - altimeter setting)*1000)+ altitude) is equal to something.
I believe that something to be pressure altitude. What I don't know is how some of the numbers are acquired. Is the altimeter setting just an arbitrary number that you plug in or is it the number that you get from ATIS. Then for the addition of altitude, is that the true altitude or the altitude measurement fed form the "arbitrary" pressure given to the altimeter?

You are correct, pressure altitude ≈ reported altitude + 1000 * (29.92 - altimeter setting) in feet and inHg.
The altimeter setting is reported by the weather station.  It is letting you know that in the vicinity of the weather station how the air is relative to a standard atmosphere (which is what all of your instruments are calibrated with respect to).
For instance, if you are on the ground at 1000 feet elevation, and the altimeter is 30.02, the pressure altitude will be approximately 1000 - 100 = 900 ft.
If you are flying at a true altitude 2000 ft (1000 ft above that same airport) and the altimeter is 30.02, your pressure altitude while flying is approximately 1900 ft.


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Is 14.29 volts too strong for a 14V DC chronograph?
I've bought a Davtron model 811B aircraft clock (14 Volts), but my power source when measured with an accurate multimeter, reads exactly 14,29 Volts. Is that a problem? I mean is that tension (14,29 V) "too strong" for a 14V avionic? Thanks a lot.

In my car that has a 12V battery, the voltage is 14.1V when the engine is running (and thus charging the battery). And when fully charged, the voltage is above 12V. I guess an aircraft shouldn't be much different.

The nominally-12V line in a car might be as high as 14.5V when the battery is being topped off after a cranking-start, and as low as ~10V while the starter is actively turning the engine over (and a weak battery on a cold morning)  This is why the console might not light up during cranking, and car audio often cuts out while cranking to avoid damage and popping sounds.

No it is not, it's within engineering tolerances of the specification. Note also that to get meaningful measurements to 4-place accuracy requires manual calibration of the measurement device to a standard, if the measurement device was not self-calibrating. .

Hi there! Thanks a lot for your prompt reply! I'm more confident to plug the chronograph in now, knowing the tolerance is ok. And another question, if I tried to light the clock up using "only" 12V instead of 14 V, would it damage the inner components? Thank you very much sir!

12V would not damage the components, but the clock itself might not run at the right speed! -NN

@nielsnielsen, The idea that the speed of a clock—we're talking about a clock that's marketed as a navigation instrument for an aircraft—would depend on the DC supply voltage is... odd.

@SolomonSlow, the context is what would be the consequence if the drive voltage is out-of-spec for the device. This sort of thing is why the specs get written in the first place. It would be rash to assume a timekeeping device designed to run on 14 VDC would meet its accuracy specs at 12 VDC unless the manufacturer explicitly said so.

If I were writing requirements for a clock that was meant for use in an aircraft cockpit, I would propose that it should go dark instead of displaying incorrect time of day. It would be easy to make the display go dark if the supply voltage fell below some arbitrary threshold, and easy enough to design the timekeeping circuitry to be reliable at a still lower supply voltage.

@SolomonSlow, that is a clever concept!

Note +0.29 V is only +2%, as already answered. This small overvoltage is likely not a problem:

I doubt the electrical generator voltage is 2% stable on an aircraft.

The accuracy doesn't depend on the exact voltage; there is a crystal-piloted oscillator.

But there is no voltage tolerance mentioned in the specs, and on the other hand it's very easy to drop the voltage in excess with a resistor.
The specs say you can use a source up to 30 V.

Model 811B operational input is 11V - 30V

Source: Davtron.
However this requires inserting a resistor in series.

The resistor drops the voltage in excess of 14 V. As the current is said to be 400 mA, for 28 V, voltage in excess is 14 V, and so the value would be $\small 14 / 0.4 = 35 Ω$. This is the value indicated in the documentation.
For 0.29 V in excess this requires $\small 0.29 / 0.4 = 0.725 Ω$. The standard value is $\small 0.75 Ω$ (with either 5% or 10% tolerance anyway). The minimum power acceptable by the resistor is ¼ W (maximum dissipated power is $\small 0.75 * 0.5^2 = 0.19 W$, more the time the fuse blows, but it's only a few ms).

With this resistor you have 14 V at the clock input. This will cost you 20 cents.

What makes you say that "the documentation is suspicious as with a resistor there is no limit actually"? If the documentation says that the upper limit is 30 V, then I certainly wouldn't connect it to 31 V or more even with a 10 kΩ resistor. A resistor doesn't drop any voltage until there's a current through it, and when you connect this device to power, there's no guarantee that it will begin drawing current before it gets damaged by the excessive voltage. (Correct me if I'm wrong. Maybe there is such a guarantee somewhere, but I would assume that there is not.)

As for the power rating, notice that for a 28 V system, the manual calls for using a resistor rated for 25 W even though the expected power dissipation is only about 9 W. That's probably on purpose! Resistors can get quite hot at their rated power, and an airplane's electrical system is a place where you particularly don't want anything to catch fire, so the recommendation to use a resistor with about 3 times the rated power makes sense.

Also note that the power rating of the resistor needs to be chosen based on the current rating of the fuse (or circuit breaker), not by the expected load current. If the current rating of the fuse is 1 A, then that 0.75 Ω fuse will produce 0.75 W of heat at that current. A derating factor of 3 may be appropriate, and so a resistor rated for 2.25 W or more may be safe. Don't take my word for it! I'm not an electrical engineer; this is all just an educated guess.

The clock uses an incandescent display, and according to the manual that's all that's powered from the aircraft. Incandescent lights are tolerant to wide ranges of voltage and therefore are hooked up unregulated, though higher voltages reduces lifetime. The resistor is just a quick and dirty way of preserving bulb lifetime.

@TannerSwett: That sounds about right; some failure mode could hypothetically pull the max current allowed by the fuse through the resistor, even if that's significantly more than the device draws in any normal state of operation.  So yes, max power is fuse current rating times resister's resistance.  In an enclosed space with poor ventilation, yeah, derate accordingly.  Or just don't mess around with a resistor at all; if aircraft electrical systems are anything like automotive, 14.29 V is remarkably close to the actual rated voltage; it's likely fine with +-1 or 2 volts.

Thank you all for the answers. I've learned a lot.... very interesting this article about how diodes could protect the circuit from over voltage. Thanks a lot


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When a VOR is an IAF, must it be treated as a fly-over waypoint, or is fly-by acceptable?
I have a VOR approach at KMDQ that has you fly outbound from the VOR as the IAF, do a procedure turn and come back to the VOR as the Final approach fix.  My question is, when you are using it as the IAF, do you have to wait for the flip on the VOR before turning outbound to line up for the procedure turn? Or can you treat it as a flyby point and start the turn before reaching it?

Depends on what equipment you have in the plane. If you have DME/GPS then you can round out your turn before the VOR. If not then you will not know your distance, therefore, you must wait for the flip. No regulation saying you must flyover the VOR.

Thanks so much.  That is what I was thinking as well, but wasn’t sure


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How many flights follow the North Atlantic Track relative to those that don't?
What is the ratio of flights that follow the track system in the north Atlantic and those that don't? Also what is the general trend in this ratio over time?

According to ICAO NAT doc 007 (North Atlantic Operations and Airspace Manual, edition 2014/2015) (PDF), approximately half of the North Atlantic (NAT) flight use the Oceanic Track System (OTS).

2.1.3: It should be appreciated, however, that use of OTS tracks is not
  mandatory. Currently about half of NAT flights utilise the OTS.
  Aircraft may fly on random routes which remain clear of the OTS or may
  fly on any route that joins or leaves an outer track of the OTS. There
  is also nothing to prevent an operator from planning a route which
  crosses the OTS. However, in this case, operators must be aware that
  whilst ATC will make every effort to clear random traffic across the
  OTS at published levels, re-routes or significant changes in flight
  level from those planned are very likely to be necessary during most
  of the OTS traffic periods.

Note that not all flights in the NAT do cross the Atlantic from East to West or vice versa. For example:

Flights from Northern Europe to Spain / Canaries / Portugal and v.v.
Flights from Portugal to the Azores and v.v.
Flights from Iceland

And then there are a number of fixed routes that allow aircraft that do no meet the minimum navigation performance requirements to cross the ocean. These tracks do not change with the daily winds like the OTS tracks.

All these are included in the 'about half'
But especially in the Northern part of the NAT airspace, covered by the Reykjavik FIR there are many random routes. According to the website of Iceavia:

In 2010, 92.3% of the traffic in the Reykjavik CTA was on random
  tracks and 7.7% was on the NAT tracks.

But that is mainly because the OTS tracks are usual south of the Reykjavik FIR.
That same page says:

In effect, where the preferred track lies within the geographical
  limits of the OTS, the operator is obliged to choose an OTS track or
  fly above or below the system. Where the preferred track lies clear of
  the OTS, the operator is free to fly it by nominating a random track.
  Trans-Atlantic tracks, therefore, fall into three categories: OTS,
  Random or Fixed.


text:
Is there a model to calculate fuel burn over the Atlantic ocean given an arbitrary aircraft identification?
Is there any accurate model that can take flight data, plane identifications and compute the amount of fuel that the aircraft would burn flying a set route over the Atlantic ocean.

seems to me that you are in search of the Breguet's equation: http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node98.html

fuel burn over water always appears to be much higher than assumed

I am sure every airline has such a model, which will include actual wind and temperature information, but it will contain proprietary data which is not publicly available, unless you have a proven interest and signed an NDA with the airframe and the engine companies. Boeing is actively marketing such software to it's customers. For first-order estimates, Federico's comment is a good start, but you will still need fuel flow and L/D values.
A range of similar software exists, but here the quality of the output depends mainly on the quality of the aircraft and engine models. While Boeing should know their aircraft well, the authors of independent software like Piano or APP have to guess the right values, but still sometimes such tools will be precise within one percent. Piano even offers a free version called Piano X, but you will need to burden yourself with a Windows installation to run it.
If you need even more precision, there are commercial packages which do this, first of all J2 Aircraft Dynamics. But this does much more; fuel flow is only a tiny aspect of the full package. Eurocontrol is supporting BADA, which is a tool for computing aircraft trajectories, but it can also compute the full flight and contains an extensive set of detailed aircraft datasets. Access to BADA is restricted, however, and you will need to acquire a license.
If you want to assemble your own tool, JBSim would be a good start. Write a wrapper which calls JBSim repeatedly and keeps track of the aircraft trajectory, and integrates the flight parameters along the way. But you will still need to get the aerodynamics and engine data from somewhere.


text:
Why is engine anti-ice used only until -40 for climb and cruise, but at all temperatures in descent?
Why is engine anti-ice secured in cruise and climb when SAT is -40 or less? Yet in descent it is turned on with visible moisture regardless of SAT.

The idea is that at SAT colder than -40, it's "too cold for ice to form." (That is itself a long discussion, but that's the conclusion the rule is based on.)
In cruise below -40 SAT, you don't need the engine anti-ice turned on, even in "visible moisture" or what seems to be such. But, somewhere in the descent, you'll get above that -40 cutoff, and at that point you do need the anti-ice, and probably quite promptly. So rather than letting you start a descent with the switches off & hoping / assuming that you'll notice when the temperature gets above -40, the rule is to turn it on when you start the descent in visible moisture so that it is on when you enter the regime that you need it.
In a climb, you turn it on when the TAT drops to +10. If you're distracted & don't get it on until the TAT reaches +5, nothing bad happens -- ice still isn't forming. Even at a TAT of 0, ice isn't forming all that fast. In a descent, you don't have that same margin of time... at -35 SAT, ice can form really fast. So we turn on the engine anti-ice for any descent in visible moisture so as to protect against the bad day when your first cue that "oh, we should have turned that on already" is your engines coughing & failing!

-40C has been traditionally defined as the temperature at which you can't encounter water in liquid form (supercooled droplets). (Recent research has found supercooled water as low as -48C, but in any case, the industry uses -40)
So, no requirement to turn cowls on below -40 while temperatures are expected to stay at least that cold in the climb/cruise case, but on a descent, you are going to be above -40 at some point soon after you start the descent, so get the cowl leading edges warm right away, especially since they aren't going to heat up as fast with the engines at idle.
Cowl anti icing is more critical than wing anti-ice, because ice forming around the cowl inlet gets shed and is rough on fan blades.
At the warm end of the temperature range, a TAT of +10 is used because you can easily get enough temperature drop in the cowl inlet at high thrust settings from the pressure drop, so +10 is used to guarantee the cowl inlet will always be above freezing when cowl A/I is off.
Even on the wings, taking off with with temps a few degrees above freezing if ground deicing wasn't used, you can have run-back water on top of the wing freeze just from the pressure drop as the wings start making lift.


text:
Can you own a fractional portion of a kitplane or experimental airplane?
I understand that experimental/kit planes can't be used for 'training for hire', i.e. an option of leasing them to flight schools is out. But... is it possible to own such aircraft on the fractional basis? Is there anything in regulations that would prevent me from holding, let's say, a 1/4 ownership of a Sling 4?

Which country's regulations are you asking about?

There is no rule against that.  As far as the FAA is concerned, at least.

Yes, at least in the United States, there is no problem doing this and quite a few aircraft clubs do exactly that.

Yes, I meant in the US. Sorry for not being specific. I'm glad to hear that the clubs take advantage of it. Thank you for all your responses.


text:
How can I isolate altitude as a specific range variable on a Sporty's electronic e6b?
So, I'm trying to understand the specific range calculation on my Sporty's E6B electronic calculator. The manual gives two examples.
In one, the assumption is 150 Ground Speed, 24 Gallons of fuel per hour and 140 gallons of fuel on board. It also assumes 12000 MSL. The answer is 875 miles.
Then there is another example: 160 GS, 27 G/Hr, 140 gallons on board, and MSL is 8000. The range changes to 855.6.
The problem is: the altitude is not an enterable variable (those others are). Entering it and adjusting in different parts of the calculator does nothing. Does anyone know how to isolate MSL as variable in this device?

I'm not sure how altitude figures into that equation... (140/24) * 150 = 875 miles. The second equation doesn't quite work out (140/27)*160 = 829 miles. Range is simply your fuel burn, fuel on board, and ground speed, unless the altitude is trying to take into account the climb/descent?

Thank you for your answer. Yes, I see this error. This is what's in the manual: Following the same sequence for a flight at 8,000 feet with
|140 gallons of fuel, a groundspeed of 165 and fuel burn of
27 gallons per hour, a specific range of 855.6 is calculated.
An additional 20 miles of range is available at 12,000 feet

TL;DR; You need to look up the burn rate in your POH.
I think you are misunderstanding the examples...
Your fuel burn rate is determined by your power setting and altitude from your charts in your POH. You need to look that up, so to calculate the range, here is what you do:
First, use your POH to look up your fuel burn for a specific power setting/manifold pressure/altitude, here is an example from a Cessna 172 POH:

You can then you can use that fuel burn rate in your calculations. A range calculation is simply:
$$
Range = {Fuel \above 1pt BurnRate} GS
$$
So using the table above, if we are cruising at 6000 feet @ 2200 RPM on a standard day we are burning 7.7 GPH. The 172 has a capacity of 53 gallons. If we are indicating 100 knots ground speed on a GPS (1knot = 1 nautical mile per hour), we can calculate our rate as:
$$
Range = {53 \above 1pt 7.7} 100 = 688
$$
The result would be 688 nautical miles (this is burning every drop of usable fuel, not taking into account VFR or IFR reserves).

Ah...that make sense. Thank you for taking time to answer this.


text:
Would turbine blade twist change if all conditions except the density of the fluid remained the same?
While designing a turbine, the blade twist is apparent from the velocity triangles, and this analysis only depends on the velocity.
However, would there be any difference for different media? When all conditions stay the same but the density of the fluid changes, would the twist stay the same?

What media/fluid are you expecting the turbine to run in?

The design is for water, but I am interested in how the design procedure (just the part for the blade twist calculations) could be tweaked for compressible flows like air or carbon dioxide, say.

Can you provide more details about which conditions remain the same? RPM, volumetric flow rate, mass flow rate, inlet pressure, outlet pressure, kinematic viscosity, dynamic viscosity, ...? Otherwise, the answer simply is: "yes the twist would change".

A classic comparison would be boat props vs aircraft at various RPM.  A higher density (viscosity) fluid would put more stress on the blade tips, hence shorter and more robustly built blades.  The amount of twist would depend on loading of props and would include chord length.  A tapered prop may have a different twist from an untapered or reverse tapered.  Diameter and RPM are also factors in loading.  And, as in aircraft, twist would also play a role in cruise efficiency or acceleration from standing still.
So there is no one rule about this going from one fluid to another (rare application).
Variations of design and performance in one fluid are much more common.


text:
Why don't commercial aircraft use all-movable tail surfaces like my RC plane?
Many conventional RC planes use control surfaces at the tail just like the image below:

You can see there is a part in front of each surface control that never moves and only the surface control itself moves.
So, I built an rc plane without that part in front of the surface control. Take a look below:

This plane I built flies really well (no aileron). So I was wondering: why commercial aircrafts or even rc planes dont use this type of rudder/elevator without the part in front of it? See: making the control surface the way I did reduces drag since you dont have a fix part at the tail that does nothing, it reduces weight cause you just need the control surface and nothing more and it is also way easier to build. I cant understand why commercial aircrafts and rc planes dont make use of this exactly same type of rudder/elevator!
Could you please tell me the reason?

Some aircraft do (for the horizontal stab). The tail in my Cessna 177 is an "all flying tail", also called a stabilator. I haven't seen this for a vertical stabilizer, which I believe is because if it ever got stuck (which sometimes happens), a full-moving vertical stab would be uncontrollable. Most aircraft don't need that much rudder/elevator authority anyway, and the structure required to do that would be significant.

@Ron Beyer  thanks. I checked the CESSNA 177 and the tail does not look like mine, it looks like a normal tail -> http://mms.tiger.tw/upload/2009-5/20095154522.jpg . Despite most aircrafts dont really need that much controls surface, on my case I realized I could easily cut my control surface in half and I would still have plenty of control. So that's another good point on my question, why most airfrats dont use the type of tail I built? I still cant understand cause this is so effective and I see no downside.

That picture is of a model airplane and isn't accurate (at least not for the 177's that have it, some did not), here is what one looks like: https://goo.gl/images/gRUxDW . The downside is that there is still a lot of force there, and there has to be structure to hold it. It isn't much on an RC plane, but you are talking literally tons of force that have to be transferred to the fuselage (for an airliner).

The Lockheed TriStar L-1011 also has an "all flying tail" or stabilator if you want to see something commercial sized. Most airliners have a tail trim system that can move the entire tail some number of degrees, and the elevator takes care of the rest.

A real Cessna Cardinal http://www.crossroadsfencing.com/airplane/painting%20pics/0917181251a.jpg  has a stabilator. @amandanovaes you linked to a picture of a toy plane.

The Piper Cherokee (and IIRC other planes derived from it) also has a stabilator.

Do you realize that your model is capable of maneuvers that (compared to it's size and speed) would tear apart not only a placid airliner but a high-performance fighter as well?

Related: last paragraph (before footnote) here: https://aviation.stackexchange.com/a/97244/34686

What is better and easier for small-scale models is not necessarily better for larger aircraft.
First, you can't say that the fixed part "does nothing". The tail is primarily a stabiliser; without it, a normal airplane will not fly at all. Only then it is a control surface, which allows it to fly well and how you want it.
Consequently, the size of the tail is primarily driven by stability considerations. For control, you need a certain amount of it and not too much more. If you have an all-moving tail, you may find that you need to move it only very slightly, or else control will become too sensitive. This is not necessarily easier to do.
From design point of view, the all-moving tail requires that the whole stabiliser was attached to a single shaft. On a small RC plane you can afford to make it of a simple wire. On a large aircraft, this translates to something bigger than your suburb water supply pipe: stabilisers of planes like A380 or An-124 are larger than wings of some airliners. Apart from the scale problem, this makes it a single point of failure, which makes it still heavier to be reliable.
Another design problem is nice aerodynamic coupling between the moving tail and the fuselage. Often designers have to invent something like this (A330):

Source
Overall, it is usually easier and lighter to make a conventional tail and attach an elevator (and rudder) to it.
Nevertheless, quite many airplanes have an all-moving stabiliser. There are several different reasons for this.

To accommodate a large range of centre of gravity (CG) locations, i.e. load distribution, and/or different aerodynamic configurations (e.g. flaps). This requires a large amount of control. But this control is typically 'slow': the load or configuration doesn't change in fractions of a second. So the tail is split between the slow all-moving part providing the so-called trim, and the fast conventional elevator. Most airliners have such arrangement, like the A330 from the above picture. But the largest ones, the An-124 and -225, don't use it: too hard. They entirely rely on the elevator.
There is rarely such a demand for the vertical tail: airplanes are more or less symmetrical, so rarely will you find an all-moving vertical stabiliser like this.
To provide easier load balance for small airplanes with reversible control, i.e. those where the control surfaces are moved by the pilot's muscle force. If you make an elevator on normal hinges, it may be quite hard to move it at high speed. Various tricks are used to make the force comfortable (which should be 'just right', not too much, not too small). But one of the straightforward solutions is to make the whole tail move about a carefully chosen axis. For smaller GA aircraft, the scale problem is not too bad yet, so many designs use this approach, for example, Piper PA28

Source
(The thing you see at the trailing edge is not a traditional elevator, it is the anti-servo tab that provides the 'just right' force).
Normal elevator control efficiency. Sometimes, airplanes just need more control than the normally-sized tail can provide. This primarily applies to agile supersonic aircraft. There are several reasons for it:

Agile manoeuvring obviously needs more control;
At supersonic speeds, pitch stability (and thus control effort) increases significantly;
Elevator efficiency falls. The thing is, at subsonic speeds, the normal elevator redistributes the airflow over the tail such that more air is affected than just the area of the elevator assumes. The relation is $\sqrt \frac{S_{elevator}}{S_{tail}}$, so if you have elevator occupying half the tail, its efficiency will not be just $0.5$, but $\sqrt 0.5 \approx 0.7$ compared to the all-moving stabilator deflected to the same angle. But at supersonic speeds this doesn't apply, and the relation is just linear. So all-moving surfaces make more sense. Occasionally, you can even find an all-moving vertical tail, like on Tu-160 (note it has all-moving horizontal tail as well):

Source

The anti-servo tab on the Piper is also used to trim the airplane.

Thanks, it took me a while to understand everything you said and I am pretty sure I totally agree with it :) One point that you didnt mention and I think is the greatest advantage of full control surface is that if you trim it you will always have the minimum drag as possible. If, for some reason, your tail is not well aligned with the main wing, I can easily trim the elevator and I will have the most efficiency as possible. On the other hand, with a wing that has a fixed stabilator if you trim the elevator you will still have a misalisgment cause of the fixed part (you cant move it to trim it

@amandanovaes, you are right, although for very small angles this is not necessarily true (it may cause less drag to change the curvature of the surface slightly than to tilt it). Also, the compromises you have to make with aerodynamic coupling of the tail to fuselage will likely offset much of the gain. But there are other advantages too, I just didn't try to list them all. For example, if you have a combination control like on airliners, you are not using up the elevator capacity for trim. And this creates control redundancy to some extent.

For a small RC plane that travels at slow speeds your design would work great.  However these type of designs have structural limitations.  For an all movable vertical and horizontal stabilizer setup all the forces exerted on the control surfaces would be transferred to a movable bearing.  This would be a single point of failure if the bearing were to fail.  Normally the vertical stabilizer or horizontal stabilizer would use several bolts to attach it to the airframe.  In some airplanes these control surfaces are welded on.  This distributes the stresses more equally.  I fly a Piper Cherokee with an all movable horizontal stabilizer (stabilator) and one of our pre-checks is to make sure there is no give in the bearing.  If the bearing was to give out we would have a bad day.

Structural limitation may be the only reason why this design I am using is not widelly used on commercial airplanes cause in every other point it's more efficient, less drag, more maneuvability... Thanks for your answer!

The fixed tail surfaces are to provide a passive weathervaning effect for stability.  If you have an all-flying tail, it tends to just want to trail into the airflow, so you need one of two things; hydraulic control, where the control surface is rigidly positioned by actuators and the control feel is by springs (The F-86 had an all flying hydraulically operated horizontal tail), or if non hydraulic, the surface needs an anti-servo tab (like the C-177 and just about every cable operated stabilator tail out there) to provide a speed sensitive restorative force that drives the surface to a certain position hand holds it there, and to provide a desirable stick force gradient (increasing force with displacement from trim speed).  The anti-servo tab also provides the pitch trim function by changing its neutral point when you adjust the trim, changing the airplane's trim speed.
There are some gliders that have all flying tails with no servo tabs, and these depend on a bungee spring in the elevator control circuit for all of their stick free pitch stability.  I used to fly a glider called an LS-1 that was like this, and the bungee wasn't particularly stiff, and the airplane was divergent in pitch if I let the stick go, but it was fine if I was holding it.
And airplane like the Cardinal or Cherokee, with a manually operated stabilator tail, would be pretty difficult to control without the anti-servo tab.  The tab's control rod is a very critical inspection item on a pre-flight.  The principal advantage of flying tails is more control authority for a given surface area (the Cardinal has MASSIVE tail power compared to similar aircraft), and the ability to fine tune the pitch feel gradient by how the anti-servo tab is geared.
Your RC airplane gets away with no anti-servo tab because the electric servos hold the surface at a given position.   Basically the same as hydraulic
controls.
The Zenith family of homebuilts use an all-flying rudder with no fixed vertical fin.  This wouldn't normally work so well without a fixed fin to provide a passive weathervaning force, but the Zenith gets away with it by having a very large fuselage vertical surface area aft of the wings. Otherwise it would have to have an anti-servo tab for the rudder in the absence of a vertical fin.

Thanks I reallly appreciate your answer, I never thought about the anti-servo you said, very clear!

Well they do to a degree.
Large commercial aircraft have considerably larger CG ranges than their smaller counterparts do in order to accommodate a wide range of loadings as well as shifts in the Cp due to compresssibility effects at high Mach numbers and changes of AoA.  To accommodate this, most airliners make use of a full moving tailplane for pitch trim, thence an additional elevator control surface is added for pitch authority by the pilot.  This offers a compromise between excellent pitch and minimal drag and weight as opposed to actuating the entire tailplane.  Now fully movable tailplanes for pitch control have been implemented before, as Ron Beyer points out in the L-1011.  But it’s not very common.

Yeap, I think trim is a good point in using the full moving tailplane cause you can trim it as you need and you will reduce the amount of drag as you with (if you have a fixed part in front of the control surface it will always be that same position and if it's not well aligned with the main wing, triming the elevator will just cause loss of efficiency). Thanks for your help!

It mostly comes down to force moving the entire control surface would require a massively beefed up connection point that would detract from the primary want of a commercial aircraft, carrying cargo, whether that be people or things. Military aircraft use it for the massive gain in maneuverability but most passengers get a might bit distressed if their 737 where to suddenly stand on its tail at the slight flick of a pilots wrist.

It may come down to force but since you have a much bigger control surface you dont need to move it that much so you can use gear reduction on your motor to move the control surface. But thanks for your contribution!


text:
Why are different distances listed for the ILS and the LOC on this approach chart?

Maybe someone has an idea why are there two separate distance values (marked in blue) for ILS and LOC approaches?

@DeepSpace What is a LOC DME? And how would you tune that? The ILS DME is tuned with the ILS LOC frequency!? It cannot be the VOR/DME (VNO) either because the difference to the ILS DME (IAV) is 0.9 NM according to the chart.

@Bianfable That's a very good point, I'll try to dig further

A very weird case, but each country can do things their own way.
The ILS FAF - GS intercept at 2700' - is 0.2 NM inside the LOC FAF. In the FMC database, the former is coded as FI01, and the latter is VI311. The LOC FAF is also 6.5 DME off of the LOC DME, identifier IAV, which corresponds to 7.4 DME off of VNO (the Vilnius VOR).
The key to seeing this is to consider how you get different distances from the VI312 IF point to the depicted FAF(s). Since VI312 is a single point in space, you can see where the two FAF's are relative to it... the ILS FAF is 0.2 NM farther away (which corresponds to it being 0.2 NM closer to the runway in the other set of blue-circled numbers.
Why the approach designer made the LOC FAF not quite coincident with the ILS glideslope intercept point, is its own question, and I have no insight there. (Totally mystified, in fact.)


text:
During an engine failure should I deploy 10° of flap or keep it clean?
Imagine I have an engine failure in cruise flight with a Cessna 152 or 172.
Should I select 10° flap to increase glide angle?
Would it give me more range to reach safety?

I am curious as to why you think flaps would make for a shallower glide angle or give you more range.  The opposite is true in both cases for any aircraft. I hope a flying instructor did not tell you this.

Well not an instructor but I read about L/D ratio (aerodynamic efficiency) and there is written that " with flaps lowered: 1- RANGE will be decreased, 2- GLIDE ANGLE will increase and 3- CLIMB ANGLE reduces. so I've got a bit confused about what it is really mean. (english is not my mother tongue so I am struggling sometimes understanding what exactly means)

My concerns was about GLIDE ANGLE in particular; if it is increased will I flying a longer distance without power?

Increased glide angle means a steeper glide angle, which means flying a shorter distance before reaching the ground.

I got it, I appreciate that. Thank you.

You keep it clean: adding flaps adds drag. You can see this in Section 3 of the Cessna POH, which includes a Maximum Glide (distance) diagram. In the C172S POH that I checked, it notes that maximum distance is achieved with:

SPEED 68 KIAS
PROPELLER WINDMILLING
FLAPS UP
ZERO WIND

(A tailwind would extend your range, but only in one direction.)
Two other points worth noting:

If the engine failure also caused an electrical failure then you won't be able to use the flaps anyway (in models with electrically operated flaps)
You might want to reduce your gliding distance if the best landing spot is relatively close by, and extending flaps is one way to do that (along with slipping, S-turns or other maneuvers, and extending the gear)

To add about landing on closer spots: I do NOT recommend 360s unless you have PLENTY of altitude and are confident you know how much you lose completing a 360 in that aircraft.  The last thing you want to do is get 1/2 way through your turn and realize you lack the altitude to hit your target, or worse: over-bank at a low altitude and airspeed and enter a deadly spin.

In general, the cleanest configuration gives the least drag and hence the maximum range at the optimum gliding speed. Flaps should be lowered (with caution) only a short time before touching the ground, in order to reduce the speed as much as possible...

And if you have a non-feathering constant-speed prop, pull it to low RPM to reduce drag.


text:
On modern commercial airliners, how much of the flight could be fully taken care of by the auto pilot?
If one wanted to, how large part of the flight could a modern commercial airliner do completely on its own? That is, if the pilot only was allowed to set things up and then leave the cockpit, from where (taxiing, take off, et cetera) and for how long would the airplane be able to handle things itself before things went out of hands?

for a routine flight probably the entire from right after takeoff down to landing, though it can't communicate with ATC

A related question: Why do we still use pilots to fly airplanes?

This should apply to the most advanced modern airliners. Older aircraft may not have all of the same automation available. The autopilot can take care of most tasks between takeoff and landing.
The pilots have to take care of starting the airplane. This includes turning on electronics, bringing up the aircraft systems, and starting the engines.
Taxiing is pretty much on the pilot, there is no automatic taxi yet on commercial airliners.
Once the aircraft is lined up with the runway, the pilot can hit the TOGA (Takeoff/Go Around) button. The plane will automatically apply the right amount of thrust for takeoff. The pilot will then rotate the plane (lift the nose) at the rotation speed (calculated before the flight), and the plane lifts off. Shortly after that, the pilot will engage the autopilot.
If the autopilot is set up to follow GPS waypoints and proper altitudes, it will be able to take care of the climb, cruise, and descent portions of the flight. The autopilot can follow the best speeds and fly through each waypoint in the flight plan.
Once the aircraft is approaching the runway, the pilot will tune the proper ILS frequency for the runway into the navigation radio. They will then engage the Approach mode, which captures the localizer (lateral navigation left/right to align with the runway) and glideslope (veritical navigation up/down to have the proper approach path). The pilot then needs to deploy the flaps and landing gear as the plane slows down for landing.
In the lowest visibility conditions, the plane is capable of the approach and touchdown on the runway all by itself. The pilot will then apply reverse thrust and brakes as needed to slow down.
Now that the plane is back on the ground, it is once again the pilot's job to exit the runway and taxi to the gate. Shutting down the engines and then the electronics will also be up to the pilot.
What is the autopilot still missing?

Responding to ATC (readback clearances, change frequencies)
Reacting to nearby traffic
Following ATC instructions (climb/descend, turn, slow/accelerate)
Reacting to emergencies or system failures
Controlling lights, flaps, landing gear

This is of course a high level view and there is so much more that goes into the flights.
Also, keep in mind that we have the technology to do much more. It just hasn't made it into service for one reason or another (lack of development and testing, not seen as important, etc.). We have UAVs that are much more automated than this. However, they are still working on how to effectively avoid other aircraft.

Might want to add engine start & shutdown, & most checklists.

wouldn't TCAS be able to resolve many traffic issues, if it resolves a climb it should climb until they are no longer on collision course

TCAS just alerts about conflicting traffic, it is up to the pilot to take action.

Great answer, +1. I would just add that although this perfectly answers the question of what real airplanes actually do right now, we have the technological capability to do a lot more. But the technology hasn't yet gone through large-scale testing or received regulatory approval. Dealing with emergencies/failures, avoiding other aircraft, and adapting to ATC instructions, weather, and other hurdles will keep pilots in the "front office" for quite some time yet.

They've worked out "how to effectively avoid other aircraft", it's getting the appropriate regulatory approval for the system that needs working out now. http://www.baesystems.com/magazine/BAES_051920/look-no-hands

I guess I meant the "working on" loosely, as in technological and/or regulatory.

@Adrian There's a whole litany of tests on that page that say "we should be able to do this eventually..." on them.  Trust me, developing those systems will take some time.  Especially considering the failure rate for any given system has to be essentially 0 to make them worthwhile...

"In the lowest visibility conditions, the plane is capable of the approach and touchdown on the runway all by itself" Capable, although we don't have the technology (Cat 3 ILS) installed at all airports. That said, Cat II probably could allow the autopilot to land the plane, if you really wanted it to.

UAVs are, actually, not (much) more automated than that. Operators still need to give most of those commands, just they give them over radio link.


text:
What happen to schedule flight when airport close for undertermined duration?
very similar to What happens to incoming flights when the airport shuts down
In the event that an airport shuts down for undetermined period, flights that already airborne would be divert to other nearby airports. What about planes those are still on the ground? Would they proceed to takeoff to land at a diversion or would they simply cancel the flights?
What about next day if the destination airport still close? Would they cancel all flights until airport reopen?

If an airport is shut down, all flight operations are ceased, with maybe the exception to police, state or medical flights. Scheduled, non-scheduled and general aviation flights will be grounded until the airport is reopened.
Flights will be cancelled or the passengers will be bused to airports in the vicinity, from where flights are able to depart, e.g. passengers that were scheduled to depart from Dortmund Airport would be bused to Paderborn Airport. But since the reason for a shutdown usually involves public safety, passengers will be rather evacuated and the flights cancelled, rather then moving them to another airport.


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May a commercial pilot transport an owner in the latter’s experimental aircraft for compensation?
Say Olive Oyl owns an RV and wants to hire Popeye, a commercial pilot, to fly her to the beach in her aircraft, which has an experimental certificate. May Popeye legally accept compensation for this flight?
One might hastily conclude that the prohibition in FAR 91.319(a)(2) applies

§ 91.319 Aircraft having experimental certificates: Operating limitations.
(a) No person may operate an aircraft that has an experimental certificate —
     (1) For other than the purpose for which the certificate was issued; or
     (2) Carrying persons or property for compensation or hire.

but at least paragraphs (e), (f), (g), and (h) of the same section make exceptions that allow for-hire use. Well known for-hire uses in experimentals include ferry flights, instruction, test flights, aerial survey, and acceptance flights.
“Operate” and related terms have technical definitions in this context, provided in FAR 1.1.

Commercial operator means a person who, for compensation or hire, engages in the carriage by aircraft in air commerce of persons or property, other than as an air carrier or foreign air carrier or under the authority of Part 375 of this title. Where it is doubtful that an operation is for “compensation or hire,” the test applied is whether the carriage by air is merely incidental to the person's other business or is, in itself, a major enterprise for profit.
Operate, with respect to aircraft, means use, cause to use or
authorize to use aircraft, for the purpose (except as provided in
§ 91.13 of this chapter) of air navigation including the piloting of aircraft, with or without the right of legal control (as owner,
lessee, or otherwise).
Operational control, with respect to a flight, means the exercise of
authority over initiating, conducting or terminating a flight.

In the scenario above, are both Olive Oyl and Popeye operating the aircraft simultaneously? Who has operational control?
Interpretation of FAA regulations seems heavily weighted in favor of protecting the ignorant public from the general risks of flying and especially from unseemly outfits who may find irresistible the temptation to cut corners. Owners and those who otherwise provide the aircraft that will carry them or their property have different incentives and receive different treatment, cf. FAR 91.319(e)(2) and FAR 91.319(g).
If Olive Oyl asserts that she is not running a commercial operation and is paying Popeye for his services, do they have a legal leg to stand on?

Is Olive Oyl a pilot as well? Who's PIC? (This could get really interesting if you were talking about something bigger that required 2 crew, and Olive hired Popeye to fill the other seat...)

This one seems pretty straightforward to me. 91.319(a)(2) applies (because in the scenario you have described the pilot would be carrying persons - Olive - for compensation or hire).
Popeye could accept compensation to reposition the aircraft (with no passengers or cargo onboard) as a ferry pilot, but not to operate the aircraft for the purposes of transporting persons or property (besides the aircraft itself and the incidental things it might carry like extra oil) - even if the person happens to be the owner of the aircraft.

Would the same rules apply if the plane was going to land at essentially the same place as where it took off, and the purpose of the flight was to allow the owner of the plane to monitor its behavior (e.g. if something in the plane rattled annoyingly while it was in the air, but the problem couldn't be identified on the ground, trying to locate the problem while someone else flew the plane would likely be much safer than trying to locate the problem while flying it).

In the scenario above, are both Olive Oyl and Popeye operating the aircraft simultaneously? Who has operational control?

Yes, technically both are "operating" the aircraft, one as the owner, and the other as the pilot. Operational control however resides with the pilot as they are the one with the responsibility and authority to initiate, conduct, and terminate a flight.

If Olive Oyl asserts that she is not running a commercial operation and is paying Popeye for his services, do they have a legal leg to stand on?

Olive here is not the one running the commercial operation, the pilot is. They are offering a service (passenger transport for hire in your aircraft), which, because the aircraft that Olive owns being an experimental, is not allowed under FAR 91.319. The pilot, being responsible for the adherence to the FAR's being a pilot, will receive the enforcement action for violating the FAR.
It is pretty cut and dried, 91.319 prohibits using an experimental category aircraft for compensation or hire for the purpose of transporting a passenger, regardless of who owns the aircraft. Additionally, if you are looking for technicalities for a loop-hole, you will find that judges will more often than not uphold the "spirit" of the law and Popeye would be prosecuted under that premise.

I do like spinach, but I'm neither a commercial pilot nor owner of an experimental. Loopholes do me no good. Commercial pilots' rule of thumb is "whose plane is it?" With the FARs, passengers aren't always passengers. It's an interesting confluence.

Under any FAR, when is a non pilot rated individual on board an aircraft not considered a passenger?

@RonBeyer When they are crewmembers.

@RonBeyer -- P.S. are you including F/E ratings when you say "pilot rated individual?" (If not, then a F/E with no pilot ratings, only a F/E rating, would be the obvious example...)

@JonathanWalters I guess I meant in the context of general aviation in the spirit of the question...

@UnrecognizedFallingObject A dying breed my friend, but you are right, a F/E or even a navigator would fall in that category.

@RonBeyer I think that's what I mean too. For example, the non-rated individual could be an observer. What if a company hired a pilot to fly an aircraft (experimental or otherwise) performing aerial survey or patrol work with a non-rated individual as a crewmember, an observer or technician for example.


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Where can I find a canonical list of sources for worldwide digital GA VFR maps?

Related question: Where can I find GA VFR maps for Australia?

For various areas of the world, where are authoritative General Aviation VFR maps, charts, and so on available on the web?

This answer is a Community Wiki. Please edit as appropriate.
Australia

OzRunways.com

United States

VFR Charts from the U.S. Federal Aviation Administration

The short answer is the most of the world is not covered very well, not even on paper charts.  Operational Navigation Charts (ONC) are available for most of the world, but they're not approved for navigation.  That said, if there's nothing else available, an ONC chart plus GPS can still be useful.


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How should I safeguard my FAA certificate number?
The FAA’s Search Airmen Certificate Information reads in part

Personal Information
We do not display your SSN, certificate number, or date of birth. We will display a releasable address in accordance with the Aviation Investment and Reform Act for the 21st Century (PDF). We display medical information based on FAA’s Civil Aerospace Medical Institute (CAMI) medical records. If the medical dates are incorrect, please contact CAMI at (405) 954-4821.

Airmen Certification Frequently Asked Questions contains the same intended exclusions.

Do you display my certificate number on the Internet?
We do not display your SSN, certificate number, or date of birth on the FAA website.

The U.S. Department of Transportation publishes an FAA Privacy Impact Assessment – Airmen/Aircraft Registry Modernization System (RMS) notes that Social Security Numbers were used in the past for certificate numbers, but policy has changed.

Personally Identifiable Information (PII) and RMS
To handle airmen certifications and aircraft registrations, FAA requires PII about airmen and aircraft owners/registrants. With this in mind, RMS may include or collect the following data on airmen and/or aircraft owners and registrants, either for authentication or certification requirements: Name, Date of birth (airmen only), Social security number (airmen only), Driver’s license number, passport number, or government ID number, Physical Description (height, weight, hair and eye color, sex, and citizenship), Address (airmen only), Medical records (airmen only), Certificate number (airmen only). In the past, RMS used an airman’s social security number as the certificate number. FAA is now changing that practice, developing unique certificate numbers not affiliated with social security number. During this change, airmen can request, online or offline, that his or her social security number not appear as a certificate number. For an individual’s PII to be included in RMS, that individual must be associated with an airmen or aircraft certificate or application.

It is clear that for airmen whose certificate numbers match their SSNs, adhering to best practices and remaining clear of practices to avoid (cf. recommendations from the Social Security Administration) are wise courses of action, primarily to reduce the risk of identity theft and fraud.
To get credit for FAA WINGS training hosted at AOPA’s Air Safety Institute, certificate number is a required field—but also one whose value ASI is careful to note that they do not store and that they pass with some level of encryption protection.
So many legal disclaimers raise red flags. What are the risks of disclosing an FAA airman certificate number? Is all the handwringing due strictly to the fact that some certificate numbers are also Social Security Numbers and nothing else? How should I protect my certificate number, which differs from my SSN?

Note: All quoted passages were retrieved from the linked resources on July 26, 2015.

I guess the question is, what can someone do maliciously if they have your certificate number, and what's the risk of that happening?
My assumption is that they can do nothing - and therefore the risk is zero - because no one uses the number for anything: it isn't needed for medicals, training, TSA approvals, flight reviews, checkrides, renting aircraft, buying insurance etc. People do want to see your certificate (and even take a copy) for various reasons, but no one will accept your certificate number by itself as proof of anything. That's my experience in the part 91 GA world anyway; I have no idea if certificate numbers are more important for airline pilots.
So my guess - and it is a guess - is that this does indeed come from when SSNs were used as certificate numbers. And as a result, unless your certificate number is also your SSN, there's probably no reason to do anything special to try to protect it.

The certificate number is not personal information unless it is SSN based, in that case the person should request a new number.  This would mitigate the value of the certificate number for the purpose of committing a fraud.
Since it provides no further leap to further personal information or access to government systems.
I would continue to show due care with personal information and think about to who you provide anything too, always ask why.  As for your certificate, it is far less invasive to provide this than a copy of your drivers license.  I wouldn't fret on this particular document since is not a key to any service.


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Why did some aircraft use hand-crank instead of gravity for alternate gear extension?
I wondered whether the final scene in The Memphis Belle where they hurry to extend the gear by hand crank (because their electric system failed) is realistic, but according to this answer the B-17 indeed used a hand crank for manual gear extension.
But why did it (and other aircraft of the era that used similar system) need to manually crank the gear all the way down rather than just pull a latch out and let gravity do the rest, like modern systems generally work?

It's realistic that the gear needed to be cranked down due to battle damage, but the urgency behind it was not. In the movie they portrayed landing with one wheel up as being instant death with the airplane exploding. It was dramatic effect, a last second click of the gear locking into place saving the crew, in reality it rarely meant more than a bent airplane having one wheel up.

@GdD, … especially since the wheel protruded quite far below the engine even in retracted position.

The B-17 used an oil filled strut that extended down and rearward, moved by a screw drive in front of the strut which also was part of the locking mechanism.  Gravity was not your friend, as disconnection of the screw drive, by battle damage for example, would let the main wheel pivot rearward into the trailing edge of the wing on landing.  The cranks were coaxial with the electric motors that swung the gear and it takes somewhat over 200 turns to get one down.  No one cranks them up.

They had to manually crank down the gear because the electric system was damaged.
"As the B-17 limps closer to base, Dearborn orders the landing gear dropped. Only one wheel descends due to electrical failure caused by battle damage, but the crew are able to manually lower the malfunctioning wheel just before landing."
Free fall only works for hydraulic powered landing gear systems. The B-17 uses an electrically driven motor to raise and lower the gear.
Not all hydraulic landing gear can free fall. PBY-5A's have hydraulic gear and emergency gear extension used a backup hydraulic pump. Additionally you could manually break the up locks and then manually push the gear to the locked position.
I bet many other WWII era aircraft with hydraulic gear were similar. Free falling hydraulic gear probably came much later.

But what is the mechanical difference between electric and hydraulic actuator that allows disconnecting a hydraulic one, but not an electric one?

Mechanical difference is that electrical systems typically use a snail gear. The snail gear only works easy from one end, but not from another.

@JanHudec Free fall on hydraulic actuators work because in free-fall model both sides of the actuator are open to return, so the hydraulic fluid can freely flow from one side of the actuator to the other. Really there is no reason you can't do free fall with electric, there would just have to a way a disengage the electric actuator from the gear. Further, some hydraulic gear actually require cranking to unlock the uplocks and to lock the downlocks,

Because of wind pressure
Disengaging locks will result in landing gear to partially open but gravity is not strong enough to make the gears lock in their extended position. Wind blast or wind pressure will oppose the movement of landing gear and to actually make the gears extend fully when main system has failed, hand crank is the better option as opposed to relying on gravity.
Also modern systems do not solely rely on gravity!

actually modern systems have to demonstrate the capability to extend the gear relying only on gravity in emergency situations.

Is there any commercial aircraft which can lower gears while relying only on gravity?

So what do the modern systems require except gravity?

@FiazHusyn, Yes. Look at pretty much every main gear on any commercial airliner they open inboard to outboard, the only thing air pressure is doing is adding friction (possible exceptions are the body gear on DC10s and 747s). Nose landing gear get some benefit from the air pressure, although it is not typically needed. For example, on the 757 when testing alternate extend on the ground, you may put up to 100# of force on the NLG to make it lock, but in the dozens of tests I've witnessed the most that was needed was a slight nudge and usually nothing was needed.

@JanHudec manual crank OR Pneumatically Operated OR High Pressure Nitrogen.
Concept is to use alternate, separate source of any fluid, stored at high pressure and activated without relying on main electric power source

@FiazHusyn, which modern one requires any of that?


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Is this the correct sequence of steps to convert from true course to compass heading?
I wanted to confirm my understanding of VFR Flight Planning/Dead Reckoning with relation to heading and course calculation. Is the below correct?

Using a plotter, draw a line from departure airport to arrival airport
Using the same plotter, get the true course (TC)
Using an E6B or similar calculator, calculate the Wind Correction Angle (WCA) which is based on Wind Direction and Speed
+ or - the WCA to/from the TC and the result will be True Heading (TH)
Using the chart, see what the Magnetic Declination is and + or - the value (West is Best [add], East is Least [subtract])
The result will be Magnetic Heading (MH)
On the day of flight, check the Compass Deviation Card to + or - the deviation from the Magnetic Heading and this will give us the Compass Heading (CH)

Yep, that's how it's done!
(If you fly the same airplane all the time, one other thing you could do is take a photo of the compass card.  That way, you have the deviation already handled and you save a step at the airport.)

Thanks @steve-v. I do have a question about the compass deviation though. Given the following deviation card, is there are formula to calculate the deviation for a given heading if that heading is not exclusively listed? E.g. our MH is 153, do we just go to the closest number on the card which is 'for 150, steer 148'. What if our MH is 165? Do we go to the deviation of 150 or 180?

FYI, I asked the above comment on Reddit as well

@Dan You could use the average of the 150 and 180 numbers.

For those interested in a formula to directly compute True heading from True course, here it is:
$$T_H =T_C + \mathrm{arcsin}\left(\frac{W_S}{\mathrm{TAS}}\cdot\mathrm{sin}(W_
D-T_C)\right)\tag{1}$$
where:

$T_H$ is the true heading
$T_C$ is the true course
$W_S$ is the wind speed
$W_D$ is the wind direction (measured with the usual convention of the direction where the wind originates from, not blow to)
$\mathrm{TAS}$ is the true airspeed

Once you've computed $T_H$ you can use it to compute ground speed $G_S$ as:
$$G_S=\frac{\mathrm{TAS}\cdot\mathrm{sin}(T_H)-W_S\cdot\mathrm{sin}(W_D)}{\mathrm{sin(T_C)}}\tag{2}$$
An equivalent, maybe less clunky, formula to get $G_S$ is:
$$G_S=\frac{\mathrm{sin}(W_D-T_H)}{\mathrm{sin}(T_H-T_C)}\cdot W_S\tag{3}$$
Finally, it can also be computed using the law of cosines as
$$G_S=\sqrt{{W_S}^2+{TAS}^2-2\cdot{W_S}\cdot{TAS}\cdot\mathrm{cos}(W_D-T_H)}\tag{4}$$
I know you're asking for magnetic heading but that's extremely complicated to compute mathematically so once you have $T_H$ you simply need to look up the magnetic deviation in your sectional chart and add it to the True heading $T_H$ (like you already mention in your question)

Aren't you making it more complicated?  The E6B does this for you, and you are simply applying wind before converting to magnetic.

As far as I'm concerned this is quicker for me. I can do it with a calculator in a matter of seconds. With a flight computer it takes more time (at least it does for me): you have to slide/rotate to find wind. Then mark it with a pencil (a-ha you have to have a pencil too). Then move it to account for TAS and sort of guess where that point falls at. Then erase the dot you made with the pencil (a-ha you have to have an eraser) . With a calculator is just one formula. Hit "=". There you have it :)

Anyway, this is just for reference, in case someone needs a precise calculation. I understand most people will favor a E6B.

Was searching the internet for exactly this and it was not as easy to find as I expected. While it may not have been the answer to the question here, I for one was happy to finally end up here and find this answer. So thank you.

As a follow-up, somewhat less happy now because the ground speed formula seems incorrect. Found the (almost) correct one here: https://www.omnicalculator.com/physics/ground-speed. ("almost correct" because it has a incorrectly positioned parenthesis)

I'll review my math to check that it's correct. My calculations and the one in the link you shared have different meanings for the wind direction though. Could it be that?

The formula for the ground speed looks correct to me but I added a few more (including one that looks like the one in the link you shared that was derived using the law of cosines). I'm not sure why it doesn't work for you. If you tell me the numbers you're trying to crunch I can help you making sense out of them


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What to do when fuel is exhausted and we are denied landing by ATC?
What to do when fuel has exhausted and we are denied landing by ATC?
If we were denied landing it means we are close to the runway, and thus if we are intending for a forced landing, the runway could have been the safest option.  With time being a constraint, what call should be made to ATC?

If the fuel is exhausted, you're going to land somewhere soon enough, with or without ATC's permission.

Closely related

Also related: Who has the higher authority, the pilot in command or ATC?

While a slightly different question, my answer to May an emergency aircraft land on a closed runway? applies to this exact situation as well.

Slightly off-topic, but could well be the reason for this question. It has always been a pet peeve of mine that in some foreign languages the ATC “approves” or “autorizes”or “permits” landing, as opposed to “clears” one to land. Therefore people assume ATC might therefore “deny” someone to land. The tower will issue a landing clearance (or not), they cannot deny anything.

Declare an emergency.

You should have declared an emergency long before your fuel was exhausted. If you haven't yet, do it now.
Land Anyway
You are authorized to do whatever it takes to get the aircraft down, worry about regulations when you are alive enough to do it. Until then, ATC will clear out anything around you, just say "declaring an emergency" and then fly the plane regardless of what ATC "authorizes" you to do or not.
The literal call to ATC will be:

KXYZ, Unable, emergency, landing now.

But only if you have time to make the call.

I agree. This is a theory examination question for RT procedures.. Students are intending to Force land in an open field as their answer Post declaring and Emergency. My suggestion was to head for the Runway.

@Aviation24by7 That's a horrid question, because not only should it never ever get to that point, ATC are never going to respond in that way. I agree with your "answer", but if you're setting the question then I think it should be changed

If ATC still doesn't authorize you to land after you declare the emergency, there is probably a Really Good Reason (tm) for it, and you may want to ask why....

@Lnafziger Short final in an engine-out glide, I'd ask "why" after I was on the ground, and not sure I could be nice about it.

You are missing the point.  If they still tell you no, there are probably even greater hazards and you would probably be better off doing something else (like land on a taxiway or off airport....).

@Lnafziger I get what you're saying, I'm not suggesting that you land on top of a preschool tour group wandering around on the runway when a taxiway or the grass looks clear, I'm saying that if the pilot judges the runway to be the safest option, that is what the pilot should do regardless of what ATC is yelling in your ear. Explaining "why" is for when you have time for conversation, not at 500 feet crossing the fence.

@Lnafziger exactly my concern with this question!

@Dan I agree it's an impossible question, but examiners are asking these probably to gauge the Student's ability to come up with the best choice, knowing these students have very less experience on the field.

In addition to Ron Beyer’s answer, no controller will deny a request from a pilot who declares an emergency.  If they ever did, they would be fired so fast it would make your head spin.  In the event of a physical hindrance ie only one runway on site which is closed, listed on NOTAMS and impeded, ie equipment, workers, etc, they would ADVISE the pilot of this but the decision to proceed is the domain of the pilot alone.

The pilot would also be well within rights to put down on a taxiway if the runway is closed.

Absolutely. The objective for every pilot is to complete the mission and that is to land the aircraft safely. Being able to do that during emergency and that to at the destination, is a magical thing to happen.


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What is the source for the "rule" forbidding configuration changes below 200ft AGL?
I keep hearing from countless instructors, and even some DPE's, that in single engine aircraft, no configuration changes are allowed below 200AGL (i.e. flaps).
Some have also stated that this is when a single engine is supposed to be stabilized, despite the 500/1000AGL rule for VMC/IMC approaches respectively.
What's confusing is this is used from instrument approaches to power-off 180's, yet I've heard people use the last notch of flaps to "bump" them to their point.
Does anyone have a source on this 200' rule? Any help is appreciated!

I've never heard of a rule like that, nor would it make any sense. You put gear up before 200ft, and you may raise or lower flaps below that for very good reasons.

Another thing to point out is that the 500/1000AGL thing is not a rule, it's just a guideline. It's a good guideline for sure, but it's not in the book.

There is no rule.  There is a convention that you should be in a stabilized condition that requires no major control inputs or power changes in the last few hundred feet.  With jets, airlines often have an operational policy that requires a stabilized approach configuration once below 1000 ft to continue with a landing.
The reason is pretty simple.  If I'm well outside a descent rate or speed parameter close to the ground, I'm forced to attempt a much more radical correction, because I don't have much time, than I would farther out.  The radical correction will, unless the pilot is very experienced and proficient on type, invariably result in an over correction, and the result is oscillation about the target parameter just as the moment of truth is approaching, and from there things get entertaining.
So in training it's a mantra that is almost universally taught that you need to be settled in on slope and on speed when getting close to the runway.  On little airplanes, a couple hundred feet, on bigger ones, maybe 500, on transports, a thousand.  The more the mass and inertial involved, the farther out you need to be settled in.
If you are sufficiently skilled and experienced on an airplane type, all this is not quite that critical, but for a newer pilot it's pretty important.
The stuff about using the last bit of flap to stretch a glide doesn't work.  It might theoretically help you make it across a ditch before touching down if you were cutting it that close with an engine failure, but more likely it just steepens the glide angle and makes things worse.

Indeed, one of the things I learned from my time in ERJ sims (traded seat time during instructor fam sessions for porting their DOS pilot training tracking app to Windows on my free time) was in fact this very valuable lesson -- get in the habit of configuring for a stabilized approach well before you have to worry about anything else during the approach.


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Why has the IO-390 not replaced the IO-360?
Having looked at the IO-390 vs IO-360, one can not help but notice that very few STCs have been done, and even fewer OEMs have fitted this engine in place of the IO-360 used in many airframes.  180 or 200 gross HP vs. 210 guaranteed net for the extra weight of dynamic crank counterweights - to me that would be a no brainer.
Why is this engine having such a struggle for acceptance?

is it cheaper, more reliable, uses less fuel, quieter, and easier to maintain, and most importantly, uses the same mechanical interface and mounting point (i.e. is it a "drop in replacement"?). If not, any of those could be a reason not to use it.

As far as STCs go, per Wikipedia "In January 2009 the base price of the IO-390-EXP version was USD$32,650".  So how many of us with planes that have a perfectly good O-360 in them really feel like spending that kind of money?  That's more than we paid for the whole plane (admittedly some years ago).

Short answer: OEMs don't see a big enough return on investment (ROI) to justify the change.
Long answer:  Getting an STC is not a simple or cheap process. It costs a lot of money. The recovery off that cost has to be factored into the sales price of the updated aircraft. And there are additional costs associated with supporting a new model of an aircraft -- supply chain, spare parts, warranty, maintenance documentation, flight manuals, etc.
Marketing has to figure how many they can sell at what price. Will it generate new sales in addition to the existing aircraft? Will it cannibalize existing a/c sales? How long will it take to recoup the cost of the change? How much will it add to the bottom line over each of the next 10 years?
Ultimately; what's the ROI? And; is there a better place to allocate our capital for a better ROI?
I'm guessing most OEMs found a better place to spend their development dollars.

Not sure how your argument applies to OEMs, since they don’t need STCs to swap out engines. Restart Cessna 182s and 206s switched to Lycomings since they are both part of Textron now. Anyone can get an STC to retrofit engines. RAM Aircraft holds the STC for a larger displacement on Lycoming O-320 engines and the replacement engine in my Cherokee makes 160 hp instead of the stock 150 hp. Since there is no STC for replacing a 360 with a 390, apparently it isn”t worth anyones time and effort.

@JScarry  A change in engine requires a change to the Type Certificate. OEMs can do that through an STC, an Amended Type Certificate (ATC), or through an all new TC. You are correct that anyone can get an STC. The restart Cessnas were getting a new TC anyway, that was the time to change the engine. Your last statement applies to both OEMs and the aftermarket. No one has seen a valid business case to do it.